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Boeing-Backed, Hybrid-Electric Commuter Plane To Hit Market In 2022 (reuters.com)
An anonymous reader quotes a report from Reuters: A Seattle-area startup, backed by the venture capital arms of Boeing and JetBlue announced plans on Thursday to bring a small hybrid-electric commuter aircraft to market by 2022. The small airliner is the first of several planes planned by Zunum Aero, which said it would seat up to 12 passengers and be powered by two electric motors, dramatically reducing the travel time and cost of trips under 1,000 miles (1,600 km). Zunum's plans and timetable underscore a rush to develop small electric aircraft based on rapidly evolving battery technology and artificial intelligence systems that avoid obstacles on a road or in the sky. In a separate but related development, Boeing said on Thursday it plans to acquire a company that specializes in electric and autonomous flight to help its own efforts to develop such aircraft. Zunum's planes would fly from thousands of small airports around big cities to cut regional travel times and costs.
I haven't seen any good information on why drone technology can't simply be scaled up in size to carry passengers. Seems like we already have the technology to solve traffic and other problems. We just need to supersize it.
Mike @ The Geek Pub. Let's Make Stuff!
no one on board to prevent passenger problems?
I've read about how planes are required to have certain amounts of fuel at certain points relative to their trip.
You need to have 100 or 200 nmi of fuel left once you reach for destination to divert if necessary. Depends on the Part and certificate under which you operate.
More to my point I have heard that this is why planes often have to dump unused jet fuel (usually conveniently done over less-desirable neighborhoods near the airport) before landing.
Planes have to have a provision to reduce weight if the plane must land before the destination. Generally, if the maximum takeoff weight (MTOW) is greater than 105% of the maximum landing weight (MLW), there will be a fuel dump option. It is not used often, only during an abnormality or declared emergency, if the type is so equipped. Otherwise, the plane will circle, if practical, to burn fuel to reduce weight for landing. If that isn't possible, an overweight landing will happen with the air frame taken out of service for a D-level inspection.
If your fuel instead is primarily batteries, how will that change these regulations?
The air frame will be designed such that MTOW = MLW. This isn't an unusual design criterion at all.
Quadcopter don't scale. I assume that's what you meant - virtually all of the toy and hobby "drones" are quadcopters.
The power produced by a propeller is proportional to it's length.
The weight of a craft, however, is proportional to it's length X width X height.
Suppose we have a toy that's 1 foot X 1 X 1. It's one cubic foot. Perhaps it weighs one pound. The 1 foot prop needs to make 1 pound of thrust.
Now we scale that "ten times bigger". Now the dimensions are 10x10x10. That's 1,000 cubic feet! "Ten times the size" is about a THOUSAND times the weight. But our prop is only ten times as long, so it makes ten times the thrust, enough to lift TEN pounds, not a thousand pounds.
In other words, as the size of craft increases, weight increases with roughly the size (length) CUBED. Prop thrust only increases directly proportional to size (length).
It's therefore therefore relatively easy to lift a small craft with props, but the power requirements go up real fast as the size increases, until you basically hit a wall of impossible physics. The largest helicopters that can be physically built carry about 40 people, whereas an A380 plane seats 853 people.
For an actuator disk of area A, with induced velocity v at the rotor disk, and with p as the density of air, the mass flow rate m through the disk area is:
m =pAv
By conservation of mass, the mass flow rate is constant across the slipstream both upstream and downstream of the disk (regardless of velocity). Since the flow far upstream of a helicopter in a level hover is at rest, the starting velocity, momentum, and energy are zero. If the homogeneous slipstream far downstream of the disk has velocity w, by conservation of momentum the total thrust T developed over the disk is equal to the rate of change of momentum, which given zero starting velocity is:
T=mw
Because tip velocity can't exceed c, w is limited to far below the transonic regime. Therefore w can't be increased beyond an easily achievable value. Meaning thrust T is limited to a (roughly) constant factor times m, mass air flow. Recall mass air flow is pAv. p, air density, we can't change. v is limited to far subsonic, so we can increase thrust T only proportionally to A, the area of the rotor disk. By middle school geometry the area of the disc is pi 2 r. Pi and 2 being constants, the area, and therefore the thrust are directly proportional to r, the radius (the length of the rotor blade),
Some ultralights and electric hang gliders can recover energy on descent. For example the Icaro is similar to designs that do this. (I haven't flown one myself.)
Theoretically you can take off on a full charge to climb into soaring conditions, turn off the motor, windmill the prop, and recharge by basically capturing the energy gained in the lift of thermals. (i.e. solar energy). Then glide to the LZ and end up with a full charge.
I can't wait to try one.
By middle school geometry the area of the disc is pi 2 r.
Shouldn't that be pi*r^2? So that your ten-foot drone would make 100 pounds of thrust, rather than 10? Of course. since 100 1000, your point still somewhat stands.
Yes, of course you're right. It's the AREA of the disk, multiplied by the velocity, which determines how much air is moved at what rate, which equals how much thrust is created (Newton's third law). I typed it as circumference rather than area.
What I didn't go into was a consideration with real props which brings it closer to directly proportional, so the actual real-life performance is in between the area and the circumference. The inner part of the blade is of course moving slower than the tips, in terms of linear speed. In other words, if the rotor tips are moving through the air at 400MPH, halfway toward the hub it's only slicing through the air at 200MPH. So the portion of the rotor which is delivering maximum power is at the ends, measured by the circumference.
Does that make sense? The total area is proportional to r^2, but the area of blade working at full speed is proportional to just r. Meaning the total thrust is between X * r and X * r^2.
Your correction points out why large rotorcraft normally use one lifting rotor rather than multiple as hobby craft often do. A single 40 foot rotor has twice the swept area of the two 20-foot rotors which would fit on the same airframe. Of course, when you need rotor too big to build and affix to the airframe, such as a heavy-lift copter, you may end up with tandem rotors simply because a 120' rotor is Impractical.
So many problems are solved by working in three dimensions. And moving up off the ground -- where dogs, children, pedestrians, sheep and every other thing you can think of lives or stands to impede and surprise -- makes many problems trivial. Line of sight to talk with other vehicles is also a bonus. I see far fewer problems to solve with an airborne autonomy than with ground based autonomy. Although other problems do materialize, of course.
Much air travel is already autonomous truth be known. But such a commuter traffic system would have to be universal. Everything in the air would need to be under control. Sorry pilots you are SOL. Sit back and enjoy the view. Have a cocktail whydoncha?
"No fear. No envy. No meanness." Liam Clancy
Even the best batteries suck in terms of energy density. Planes require a lot of fuel. Batteries are heavy. Planes need light loads. The carbon composite airframes help to a degree but this is something that can be applied to traditional aircraft.
I could see fuel cells working. Or electric generation. Nothing wrong with electric motors. Batteries seem like a dead end though.
I watched the great video and was disappointed that their prices link is broken. It uses a folding prop so I don't see how it could recover energy, and anyway a powered hang glider isn't going to need to increase drag to descend.
http://michaelsmith.id.au
Also, force is not power.
The models that do energy recovery have an option to fold the prop or not.
And yes most hang gliders don't really need more drag. Most pilots would rather fly longer and just recharge the battery on the ground. It isn't like it is very expensive.
There are conditions where you can get really high and you're tired and just want to get down. A speed brake would be useful then.
The big reason most helicopters have one rotor is simplicity in design, maintenance, and control.
Also, I'm not sure about your reasoning on thrust being nearly proportional to blade length. At any given tip speed, the proportion of any blade length running within any given range of speed is the same no matter what size the rotor, and the maximum tip speed is fixed regardless of the size. In addition, the longer the blades (for a given amount of lift), the more efficient they are.
There are trade-offs among lift, blade length, bending moment, structural strength and weight, etc., that limit rotor diameter, but you don't go into those.
batteries get heavier as they discharge...
Instinctively this just sounds wrong.
I mean seriously wrong!
Even if electrons had negative mass, and were actually 'used up' in providing power, I'd still think something were wrong...
Can someone help me out here?
For fixed-wing craft (airplanes) blade tips CAN as you say, go supersonic, though that's quite rare because there is an enormous increase in drag at transonic speeds. Helicopters not only have the large increase in drag to worry about, but also in forward flight one wing is moving forward while the other wing in moving backward.
Consider the world's fastest military helicopter, the Chinook, flying forward at 315km/h. If the blade tip were moving at 1,000 km/h relative to the fuselage, the advancing blade would be moving through the air at 1,315, or Mach 1.1, while the retreating blade on the other side would have airspeed of 685 km/h. That would mean the advancing side of the rotor would be going twice as fast as the retreating side. You can imagine how it's pretty much impossible to design a rotor that can be moving at both supersonic speeds and very subsonic at the same time.
Additionally the blade tips at times enter the vortex of the other blade, which will cause local transonic flow, and disruption of the aerodynamics, if the "normal" velocity is even close to the speed of sound.
Practical designs for regular use are therefore limited to well under the speed of sound at the tips. This is no great loss because rotor drag is a function of the CUBE of the speed. While lift increases with the square of diameter, drag increases with the cube, so a large, slow rotor is better anyway.
> Also, I'm not sure about your reasoning on thrust being nearly proportional to blade length.
By Newton's third law, thrust is equal to the force applied to the air moved through the rotor disc. That's the area of the rotor disc times the average acceleration of the air (average velocity change). There are two terms there, disc area and AVERAGE Delta V of the air.
The disc area is proportional to the square of the rotor radius. On the other hand, the portion of the rotor near the hub has nearly zero linear velocity, and flows very little air. The majority of the thrust is generated nearer the rotor tips. The area of high thrust, say within 8 feet of the rotor tip, is essentially the circumference of the disc, and therefore linearly proportional to the rotor diameter.
So one term is linearly proportional to the rotor radius, one term to the square of the radius.
>. The big reason most helicopters have one rotor is simplicity in design, maintenance, and control.
A single 40 foot rotor has 4 times the disc area of two 20 foot rotors. Because thrust is the disc area multiplied by the average delta V, four times as much swept area makes a big difference in thrust. The one large rotor makes much more thrust than two rotors of half the diameter.
It does bother me that the wing and keel are in the plane of the prop. If it sheds a blade, how much of a wing will you be left with?
http://michaelsmith.id.au
If the prop actually does break and hits the fabric of the wing it will probably punch a hole. The sailcloth is pretty tough and doesn't rip that easily. I would expect degraded flight but not plummeting out of the sky. If wing damage did occur you would probably end up with an asymmetrical wing and worst case end up with an uncontrollable turn. That's the time to throw the chute which has a pivot joint exactly for that reason.